Reassessment of the earliest documented stegosaurian fossils from Asia     

《Cretaceous Research》2016

In 1929, the famous Swedish palaeontologist Carl Wiman documented the first unequivocal stegosaurian dinosaur fossils from Asia. His material comprised an isolated dermal spine, together with a dorsal vertebra that was briefly described but never figured. Since then these remains have languished in obscurity, being noted in some stegosaur review articles but often ignored altogether. However, recent auditing of the Museum of Evolution palaeontological collection at Uppsala University in Sweden has led to the rediscovery of Wiman's original specimens, as well as two additional previously unrecognised stegosaurian dorsal vertebrae. All of these bones derive from the Lower Cretaceous (Berriasian–Valanginian) Mengyin Formation of Shandong Province in eastern China, and are morphologically compatible with the stratigraphically proximal stegosaurian taxon Wuerhosaurus from the Valanginian–Albian Tugulu Group in the Xinjiang Uyghur Autonomous Region of Western China. Wiman's seminal stegosaurian fossils thus expand current palaeobiogeographical distributions, and contribute to the otherwise enigmatic record of Early Cretaceous stegosaurian occurrences globally.  相似文献   

The Western Sierras Pampeanas: Protracted Grenville-age history (1330–1030 Ma) of intra-oceanic arcs,subduction–accretion at continental-edge and AMCG intraplate magmatism     

C.W. Rapela  R.J. Pankhurst  C. Casquet  E. Baldo  C. Galindo  C.M. Fanning  J.M. Dahlquist 《Journal of South American Earth Sciences》2010,29(1):105-127

New U–Pb SHRIMP zircon ages combined with geochemical and isotope investigation in the Sierra de Maz and Sierra de Pie de Palo and a xenolith of the Precordillera basement (Ullún), provides insight into the identification of major Grenville-age tectonomagmatic events and their timing in the Western Sierras Pampeanas. The study reveals two contrasting scenarios that evolved separately during the 300 Ma long history: Sierra de Maz, which was always part of a continental crust, and the juvenile oceanic arc and back-arc sector of Sierra de Pie de Palo and Ullún. The oldest rocks are the Andino-type granitic orthogneisses of Sierra de Maz (1330–1260 Ma) and associated subalkaline basic rocks, that were part of an active continental margin developed in a Paleoproterozoic crust. Amphibolite facies metamorphism affected the orthogneisses at ca. 1175 Ma, while granulite facies was attained in neighbouring meta-sediments and basic granulites. Interruption of continental-edge magmatism and high-grade metamorphism is interpreted as related to an arc–continental collision dated by zircon overgrowths at 1170–1230 Ma. The next event consisted of massif-type anorthosites and related meta-jotunites, meta-mangerites (1092 ± 6 Ma) and meta-granites (1086 ± 10 Ma) that define an AMCG complex in Sierra de Maz. The emplacement of these mantle-derived magmas during an extensional episode produced a widespread thermal overprint at ca. 1095 Ma in neighbouring country rocks. In constrast, juvenile oceanic arc and back-arc complexes dominated the Sierra de Pie de Palo–Ullún sector, that was fully developed ca. 1200 Ma (1196 ± 8 Ma metagabbro). A new episode of oceanic arc magmatism at ～1165 Ma was roughly coeval with the amphibolite high-grade metamorphism of Sierra de Maz, indicating that these two sectors underwent independent geodynamic scenarios at this age. Two more episodes of arc subduction are registered in the Pie de Palo–Ullún sector: (i) 1110 ± 10 Ma orthogneisses and basic amphibolites with geochemical fingerprints of emplacement in a more mature crust, and (ii) a 1027 ± 17 Ma TTG juvenile suite, which is the youngest Grenville-age magmatic event registered in the Western Sierras Pampeanas. The geodynamic history in both study areas reveals a complex orogenic evolution, dominated by convergent tectonics and accretion of juvenile oceanic arcs to the continent.  相似文献   

A geochemical clogging model with carbonate precipitation rates under hydrothermal conditions     

《Applied Geochemistry》2013

A step-wise numerical calculation method was developed to provide predictions of when and where carbonate deposits might be found through reservoirs during CO₂ sequestration. Flow experiments through porous media using a supersaturated carbonate fluid were also performed in order to observe flow rates. In order to evaluate precipitation rates and permeability change in the formation, calculated flow rates based on the proposed geochemical clogging model were compared with the experimentally observed data. Both high and low temperature cases were studied to understand how hydrothermal conditions can affect precipitation rates of carbonate. According to chemical kinetics, growth rates of minerals are generally proportional to the saturation index (S.I.) that depends on temperature. Thus, a supersaturated fluid has the advantage of improving the filtration and the amount of C fixation (σ). However, when the ratio of filtration coefficient (λ) to pore fluid velocity (u) increases, the permeability around the injection point tends to be significantly reduced by carbonate accumulation, and thus, this might result in insufficient injection of CO₂. Therefore, it is essential to understand how to control both λ and u so that the precipitation of carbonate can be located as far away from the inlet as possible.  相似文献   

Multivariate statistical analysis of underground gas storage caverns on groundwater chemistry in Korea     

Jeonghoon Lee  Kyung‐Seok Ko  Jun‐Mo Kim  Ho‐Wan Chang 《水文研究》2008,22(17):3410-3417

An understanding of groundwater flow and chemistry is important to operate underground storage caverns. Groundwater flow is mainly affected by cavern operating conditions. Groundwater chemistry is modified by disinfection activities for removing possible biological clogging and by mixing with cement pore water. It is important to discern these two effects, because wells affected by the disinfection activities may have hydrological connections with water curtains used to inject the disinfectant. However, it is difficult to separate these two effects using graphical methods because of their similar chemical characteristics. Instead, multivariate statistical analysis, such as principal component analysis (PCA) and factor analysis (FA), can be used. Groundwater samples for chemical analysis were obtained from four surveys in 1999–2000. Based on the results from PCA and FA, it appears that there were temporal variations of seepage water into the propane area when the cavern operation fluctuated, but we could not observe such variation in the butane area. These changes may occur mainly at depth, where water flow is slow and water renewal in the cavern surrounding is limited. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Thermal profiles inferred from fluid inclusion and illite geothermometry from sandstones of the Athabasca basin: Implications for fluid flow and unconformity-related uranium mineralization     

《Ore Geology Reviews》2016

The Proterozoic Athabasca basin and underlying basement host numerous unconformity-related uranium deposits that were formed from extensive fluid circulation near the basement-cover interface. Although it is generally agreed that the mineralizing fluids were basinal brines, it is still unclear what driving forces were responsible for the circulation of the basinal fluids. Because different fluid flow driving forces are associated with different thermal profiles, knowing the basin-scale distribution of paleo-fluid temperatures can help constrain the fluid flow mechanism. This study uses fluid inclusions entrapped in quartz overgrowths and authigenic illite in sandstones from three drill cores (WC-79-1, BL-08-01, and DV10-001) in the central part of the Athabasca basin as thermal indicators of paleo-fluids in the basin. A total of 342 fluid inclusions in quartz overgrowths were studied for microthermometry. The homogenization temperatures (T_h) range from 50° to 235 °C, recording the minimum temperatures in various diagenetic stages. Temperatures estimated from illite geothermometry (121 points) range from 212° to 298 °C, which are systematically higher than (partly overlapping) the T_h values, suggesting that illite was precipitated in hotter fluids following the formation of quartz overgrowths. Neither the fluid inclusion T_h values nor the illite temperatures show systematic increase with depth in individual drill cores. This, together with the high illite temperatures that cannot be explained by burial at a normal geothermal gradient (35 °C/km), is interpreted to indicate that basin-scale fluid convection took place during the diagenetic history of the basin. Prolonged fluid convection is inferred to be responsible for delivering uranium (extracted from the basin or the upper part of the basement) to the unconformity, where uranium mineralization took place due to redox reactions associated with fluid-rock interaction or structurally controlled fluid mixing.  相似文献   

Geology,geochemistry, and genesis of Axi: A Paleozoic low-sulfidation type epithermal gold deposit in Xinjiang,China     

《Ore Geology Reviews》2010,37(4):265-281

Axi is a low-sulfidation type epithermal gold deposit hosted in Paleozoic subaerial volcanic rocks in the western Tianshan orogenic belt, Xinjiang, China. The resource is more than 50 t gold at an average grade of > 4.4 ppm. The deposit occurs in the Tulasu volcanic fault-basin in the Paleozoic active continental margin on the northern side of the Yili-Central Tianshan plate. The host rocks are andesitic volcaniclastic rocks of the Paleozoic Dahalajunshan Formation, and the orebodies occur as veins in annular faults of a paleocaldera. Mineralization at Axi can be subdivided into five stages: quartz and/or chalcedony vein, quartz vein, quartz-carbonate vein, sulfide vein and carbonate vein. There are two types of ore host: quartz vein and altered rocks. Ore minerals are native gold, electrum, pyrite, marcasite, arsenopyrite, hematite, limonite, and trace amounts of pyrargyrite, polybasite, naumannite, cerargyrite, sphalerite, chalcopyrite, tetrahedrite, galena, pyrrhotite and clausthalite; gangue minerals are mainly quartz, chalcedony, illite, calcite, siderite, dolomite, adularia and laumontite. The main wall-rock alteration is silicification and phyllic alteration, carbonatization and propylitization. The deposit is characterized by an enrichment, relative to crustal abundance, of Au, Ag, As, Sb, Bi, Hg, Se, Te and Mo, depletion in base metals (Cu, Pb, and Zn), and a low Ag/Au ratio (0.5–3.7).Three types of fluid inclusions were recognized in quartz from the major mineralization stages: liquid aqueous inclusions, liquid-rich two-phase inclusions and small amounts of vapor-rich two-phase inclusions. Microthermometric measurements indicate that the final ice melting temperatures are − 0.3 to − 4.4 °C, corresponding to salinities of 0.5–6.9 wt.% NaCl equiv. (2.2 wt.% NaCl equiv. in average). The peak temperatures of ice melting varies from − 0.4 to − 1.9 °C, corresponding to salinities of 0.7–3.1 wt.% NaCl equiv. Homogenization temperatures range mainly between 120 and 240 °C, with an average of 190 °C and a maximum of 335 °C. The fluid density is 0.73 to 0.95 g/cm³ and thus the estimated maximum mineralization depth is about 700 m.Hydrogen and oxygen isotopic compositions of the ore fluids lie within a narrow range: δD_H2O is − 98 to − 116‰ and δ¹⁸O_H2O − 1.8 to 0.4‰. ³He/⁴He ranges from 0.0218 to 0.138 Ra, with an average of 0.044 Ra, indicating that He derived predominantly from crust with negligible mantle He in the ore fluids. By contrast, the ⁴⁰Ar/³⁶Ar ranges from 317.7 to 866.0, suggesting that crust-derived radioactive ⁴⁰Ar⁎ accounts for 7.0 to 66%, and atmospheric ⁴⁰Ar about 43 to 93% in the ore fluids. Hydrogen, oxygen, carbon, sulfur and noble gas isotopes indicate that the ore-forming fluids of the Axi gold deposit consisted predominantly of circulating meteoric water. Ore-forming metals may have derived mainly from the host volcaniclastic rocks of the Dahalajunshan Formation and basement rocks. The occurrence of adularia, platy calcite, and quartz or sulfide aggregates as pseudomorphs after bladed calcite in ore veins, and occurrence of aqueous liquid, and liquid-rich and vapor-rich two-phase inclusions, indicates that boiling of the ore-forming fluid have occurred, leading to supersaturation of the hydrothermal solution and deposition of ore metals. This is the main mineralization mechanism for quartz-vein type ores in Axi. The ore-forming fluid was buffered to a near-neutral pH in a reduced environment during mineralization. The preservation of this Paleozoic Axi deposit and its discovery required a rapid accumulation of sediments in the basin after formation of the deposit, and minimal amount of erosion after Late Cenozoic uplift.  相似文献   

Geophysical evidence for an extensive Pie de Palo Complex mafic–ultramafic belt,San Juan,Argentina     

《Journal of South American Earth Sciences》2010,29(4):325-332

The recent completion of a high-resolution aeromagnetic survey over the Pie de Palo uplift of the western Sierras Pampeanas has revealed an area of large magnetic anomalies associated with the Pie de Palo Complex. The Las Pirquitas thrust, which has transported and uplifted the Pie de Palo Complex, is recognized for at least 30 km in a roughly NE direction along the western boundary of the Pie de Palo Complex, beyond its limited outcrop. The type of sediments of the Caucete Group in the footwall of the Las Pirquitas thrust, which are regarded as the leading edge of the Precordillera terrane, are associated with much less pronounced magnetic anomalies.In addition, a conspicuous, NNE trending, broad magnetic high stands out in the survey, several kilometers to the east of the main outcrops of the Pie de Palo Complex; this broad magnetic anomaly bisects the Pie de Palo basement block, and continues further south at least as far as 32°S, the southern boundary of the latest aeromagnetic survey. This magnetic anomaly is interpreted to represent a structure corresponding to the Grenvillian Precordillera–Pie de Palo tectonic boundary zone, and would comprise the buried largest part of the mafic–ultramafic belt.The geophysical model of the magnetic data indicates that the boundary zone dips to the east, possibly suggesting the existence of a set of synthetic east dipping, west-verging thrusts, of which only one major structure (Las Pirquitas thrust) is exposed; the possibility of other slivers of upthrust boundary zone material cannot be excluded. It is considered that the Pie de Palo Complex represents a small sliver upthrust from the unexposed boundary zone material (containing highly magnetic mafic–ultramafic rocks).The east-dipping, west verging structures associated with the Pie de Palo Complex are suggested to represent an Ordovician reactivation of a Grenvillian suture zone developed when the Precordillera basement and Pie de Palo terrane docked; this reactivation probably resulted from the collision of the Cuyania terrane onto the western margin of Gondwana.  相似文献   

Possible two-stage ⁸⁷Sr evolution in the Stockdale Rhyolite     

W. Compston  I. McDougall  D. Wyborn 《Earth and Planetary Science Letters》1982,61(2):297-302

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Geochemistry and iron isotope systematics of coexisting Fe-bearing minerals in magmatic FeTi deposits: A case study of the Damiao titanomagnetite ore deposit,North China Craton     

《Gondwana Research》2020

Geochemical and iron isotopic compositions of magnetite, ilmenite and pyrite separates from the FeTi oxide ores hosted in the Damiao anorthosite-type FeTi ore deposit were analyzed to investigate sub-solidus cooling history of the titanomagnetite. The FeTi oxides form two series of solid solutions, namely, ulvöspinel-magnetite (Usp-Mt_ss) and hematite-ilmenite (Hem-Ilm_ss) solid solutions. The magnetite separates have 14–27 mol% ulvöspinel, while the ilmenite separates have 5–8 mol% hematite. Major element compositions of the mineral separates suggest that the ilmenites were mainly exsolved from the Usp-Mt_ss by oxidation of ulvöspinel in the temperature range of ~820–600 °C and experienced inter-oxide re-equilibration with the magnetites. Associated with the exsolution is the substantial inter-mineral iron isotope fractionation. The magnetite separates are characterized by high δ⁵⁷Fe (+0.27 − +0.65‰), whereas the ilmenite separates have lower δ⁵⁷Fe (−0.65 to −0.28‰). Two types of pyrite are petrographically observed, each of which has a distinctive iron isotope fingerprint. Type I pyrite (pyrite_I) with higher δ⁵⁷Fe (δ⁵⁷Fe = +0.63 − +0.95‰) is consistent with magmatic origin, and type II pyrite (pyrite_II) with lower δ⁵⁷Fe (δ⁵⁷Fe = −0.90 to −0.11‰) was likely to have precipitated from fluids. Iron isotopic fingerprints of the pyrite_I probably indicate variations of oxygen fugacity, whereas those of the pyrite_II may result from fluid activities. The iron isotopic fractionation between the magnetite and ilmenite is the net result of sub-solidus processes (including ulvöspinel oxidation and inter-oxide re-equilibration) without needing varying oxygen fugacity albeit its presence. Although varying composition of magnetite-ilmenite pairs reflects variations of oxygen fugacity, inter-oxide iron isotopic fractionation does not.  相似文献   

Late Carboniferous to Early Permian oceanic subduction in central Inner Mongolia and its correlation with the tectonic evolution of the southeastern Central Asian Orogenic Belt     

《Gondwana Research》2020

The Late Paleozoic magmatism in central Inner Mongolia provides important insights on the tectonic evolution and crustal growth in the Central Asian Orogenic Belt (CAOB), which formed due to the closure of the Paleo-Asian Ocean (PAO). This paper presents new zircon UPb ages and Hf isotopic compositions as well as whole-rock geochemical data on a suite of volcanic rocks from the Late Paleozoic Baoligaomiao Formation and coeval intrusions in the Baiyinwula region of the Mongolian Arc. This study revealed that the magmatic sequences evolution includes: (1) early andesites (317–311 Ma) with enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HSFEs), and positive zircon ε_Hf (t) values from +9.0 to +15.5, indicating a derivation from enriched mantle; (2) felsic rocks emplaced from 306 Ma to 292 Ma, with relatively lower ε_Hf (t) values from +6.3 to +11.3, implying juvenile crust as the primary magma source; and (3) A-type igneous rocks (280–278 Ma). The comparison of palaeontological, lithostratigraphical, and magmatic evolution in Late Paleozoic between different tectonic units in the eastern part of CAOB has displayed that the subduction of Paleo-Asian oceanic crust caused the opening of the Hegenshan Ocean along the southern margin of Mongolian Arc in Devonian; and the Baoligaomiao Formation volcanic rocks and coeval intrusions have recorded early northwards subduction and subsequent slab rollback of Hegenshan oceanic crust.  相似文献